On Wednesday, Pfizer announced that its first participant had entered the second of a three-phase study of the oral antiviral that’s intended to keep people who aren’t at risk of developing serious illness after contracting COVID-19 out of the hospital. A similar study for people who are at an increased risk began in July. While the antiviral could mark another milestone in the COVID-19 pandemic, it’ll likely be months before it’s available to the public.

The potential treatment is designed to be administered in 12-hour increments for five days in people who are symptomatic but not hospitalized. A total of 1,140 participants will be enrolled, and they’ll be given either the oral antiviral or a placebo.

The antiviral is intended to block SARS-CoV-2 from replicating. By taking it in conjunction with ritonavir, an antiretroviral agent often used to help treat HIV, the goal is to slow the breakdown of the oral antiviral so that it can remain in the body longer and work continually to combat the virus.